Different devices and methods exist for forming of a work piece. During hydroforming, for example, a tubular work piece is filled with a liquid, generally water, and sealed. By increasing the liquid pressure, the work piece is widened and gradually comes against the contours of the forming guide surrounding the work piece. In this method, relatively high forces must be applied to deform the work piece and to keep the forming die applied over a longer period. In order to obtain good results, the trend of the forces, over time, must be precisely controlled.
Hydroforming can also be operated by explosion energy. This widespread method utilizes a liquid, like water, as transfer medium for the pressure waves formed by the explosion. The work piece, generally a sheet metal plate, is positioned on the cavity of a mold and lowered into a water bath. A vacuum is generally created in the cavity beneath the work piece. By introduction of an explosive charge into the water bath and then ignition, the sheet metal plate is forced into the mold and thus acquires its final shape. This method is used, for example, in shipbuilding. It is generally used to produce flat objects to be formed from a flat plate.
An explosive forming method of the generic type just mentioned without liquid is described in EP 592 068. To produce a camshaft, a lower mold half is equipped with the already prefabricated cam. After a camshaft, hollow on the inside, has been introduced through the openings of the individual cams, the upper mold half is placed on the lower one. The individual cams are separately supported by holding arms guided through special openings in the die halves. The ends of the closed mold are sealed by sealing elements running radially to the camshaft through the side walls of the die. A plug-like spark plug, extending into the camshaft, is screwed through one of these end plates. After the shaft has been filled with combustible gas, it is ignited by means of the spark plug. Because of the abrupt increase in gas pressure in the interior of the shaft, it is widened and forced into the openings of the individual cams. These are therefore connected axially and splined to the camshaft.
This method, although it gets by without any liquid, is relatively complicated and time-consuming to handle. The mold must be initially pre-equipped with finished parts and the camshaft then threaded with precise fit through the openings of the individual cams. The side surfaces must then be applied with precise fit and mounted. Feed lines for the gas must be provided, as well as a spark plug. All these are time-intensive individual working steps. The end plates or side surfaces must be resealed either during each deformation process or provided with a sealing element. However, the latter is a part subject to wear, which causes additional costs. This complicated handling results in high time expenditure and therefore costs. This method, consequently, has not gained acceptance industrially.
It would be desirable to provide a method and device that overcome at least some of the disadvantages of the prior art.